1. Field
The disclosed embodiments lie within the field of windshield wipers and relates more specifically to windshield wipers for aircraft.
2. Brief Description of Related Developments
In the aeronautical field, in order to allow the pilot to see the external surroundings of the airplane, the cockpit is fitted with various windows and, in particular, with one or more front windows forming the windshield. These front windows, of which there are generally two in commercial airplanes, have hitherto conventionally been planar in shape, and their aerodynamic continuity with the fuselage at their periphery is provided by a seal.
In rainy weather, water flowing over the front window or windows, and insect impacts, may reduce visibility for pilots particularly during take offs, landings and taxiing. Hence, windshield wipers are fitted on the outside of these front windows. The way these work by cyclically sweeping an arc of a disk across the window using a wiper blade generally perpendicular to this arc and carrying a blade element is known, and similar for example to that of motor vehicles.
The windshield wiper blade therefore, during this cyclic sweep, covers a zone known as the wiping zone. For optimal wiping, contact between the blade element and the windshield needs to be sustained and uniform along the entire length of the blade, and needs to remain so throughout wiping.
In phases of non-use, for reasons of visibility, these windshield wipers are stored in a rest position generally situated on a (vertical or horizontal) edge of the wiping zone known as the storage position.
Elements of low rigidity, such as the seal, may be situated in the zone swept by the blade element of the windshield wiper during normal wiping (the wiping zone overlapping the seal in order to wipe a maximum zone of the window) or during its transition from the wiping zone to this storage position or vice versa, and may therefore be damaged as the blade element repeatedly passes over it. The consequence of this is both damage to the seal and therefore reduction in its effectiveness, and aerodynamic drag that also carries with it the possibility of damage to the transparencies.
For aerodynamic reasons, the design of airplane windshields is evolving toward a shape with a dual curvature, rather than the previous planar shape. This also makes it possible to increase the volume of the instrument panel behind the windshield while at the same time limiting the aerodynamic impact.
This dual curvature shape is characterized by a transverse curvature of the windshield, which starts out fairly pronounced near the lateral part of the fuselage and then becomes gentler near the central part of the fuselage, as viewed head-on, by a longitudinal curvature over the entire height of the windshield, blending into the overall shape of the fuselage.
Windshield wipers comprising rigid blade elements, suited to planar surfaces, are no longer suitable for these curved shapes because contact between the windshield and the blade element is no longer achieved over the entire surface of the wiper blade during the complete wipe.
An articulated windshield wiper of the conventional whiffletree type (FIGS. 1a and 1b) as used on motor vehicles, is better suited because its blade element tolerates a variation in curvature of the windshield during wiping.
However, there is a risk that contact between the blade element and the windshield will be interrupted momentarily, either fully or in part, at high aircraft speeds, because of the air flow.
In addition, this type of windshield wiper provides no solution to the problem of potential damage to the seal or seals and to the front glass during wiping or transitions to or from the windshield wiper storage position.
What is more, if the transition involves a lifting of the arm (FIG. 1c) before it is stored, the operation of the whiffletree leads, during lifting, to the two ends of the blade element remaining in contact with the windshield, and this is likely to cause local damage to this windshield or damage to the blade element itself.